Evaluation of hybrid PET/CT imaging with the 68Ga-labelled PSMA ligand in patients with prostate cancer and biochemical progression in the low-range values of PSA after radical prostatectomy

Abstract

Introduction: Currently 68 Ga-PSMA PET/CT is making a significant shift in the diagnosis, staging and restaging of prostate cancer (PC) patients. Мany questions have been raised concerning the indications and the sensitivity of the method. Most of them are related to the PSA values in biochemical progression, specifically in the low PSA values of up to 2.00 ng/mL. Aim: The aim of this study was to analyze the influence of PSA values in biochemical progression on 68 Ga-PSMA PET/CT sensitivity, detection rate and the association with regional or metastatic lesions incidence in patients after radical prostatectomy (RP) with a focus on the impact of the lower ranges of the PSA values. Material and Methods: We performed a retrospective analysis in 144 consecutive patients with radical prostatectomy (RP) who underwent 68 Ga-PSMA PET/CT from July 2019 to February 2020. The patients were divided into six groups according to the PSA value: 1) ≤ 0.040 ng/mL; 2) 0.041–0.160 ng/mL; 3) 0.161–0.500 ng/mL; 4) 0.501–1.0 ng/mL; 5) 1.001–2.00 ng/mL; 6) > 2.00 ng/mL. Results and Discussion: The mean age of the patients was 67.3 (7) years and the mean PSA level was 11.0 (52.28) ng/mL. A total of 62 patients (43.1%) showed at least one positive lesion. 68 Ga-PSMA PET/CT detection rate varied into the different groups between 12.0% and 94.0%. There was a significant relationship between the PSA level and the ability of 68 Ga-PSMA PET/CT to detect the lesions. Local recurrence was determined in patients with higher PSA values. Regional metastatic lymph nodes incidence in the 6 groups was between 17.0% and 50.0%. Bone metastases were most commonly diagnosed in patients with low PSA levels. Distant lymph nodes involvement in the studied groups ranged between 0.0% and 75.0%. Distant metastases were detected most commonly in patients with low levels of PSA. The PSA-based assessment of the overall sensitivity and specificity of 68 Ga-PSMA PET/CT was 58.0% and 87.0%, respectively. Sensitivity of 15.0% was found in the group with the lowest mean PSA levels. Conclusion: Tumor detection rate is positively associated with PSA levels. Biochemical progression after RP is more commonly related to distant metastases, specifically bone metastases in patients with lower levels of PSA.